Passive flow modulation of cooling flow into a cavity

ABSTRACT

A passive flow modulation device according to an embodiment includes: a temperature sensitive element disposed within a first area; a piston coupled to the temperature sensitive element, the piston extending through a wall to a second area, wherein the first area is at a higher temperature than the second area; and a valve arrangement disposed in the second area and actuated by a distal end portion of the piston, the valve arrangement tangentially injecting a supply of cooling air through an angled orifice from the second area into the first area in response an increase in temperature in the first area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending US application numbers: ______, GE docket numbers 280848-1 and 283683-1, filed on ______.

BACKGROUND OF THE INVENTION

The disclosure relates generally to turbomachines, and more particularly, to passive flow modulation of cooling flow into a cavity.

Turbines are widely used in a variety of aviation, industrial, and power generation applications to perform work. Such turbines generally include alternating stages of peripherally mounted stator vanes and rotating blades. The stator vanes may be attached to a stationary component such as a casing that surrounds the turbine, and the rotating blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as steam, combustion gases, or air, flows along a gas path through the turbine to produce work. The stator vanes accelerate and direct the compressed working fluid onto a subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work.

Various components (e.g., blades, nozzles, shrouds, etc.) and areas wheelspaces between stator and rotor) of turbines are typically cooled in some fashion to remove heat transferred by the hot gas path. A gas such as compressed air from an upstream compressor may be supplied through at least one cooling circuit including one or more cooling passages to cool the turbine.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a passive flow modulation device, including: a temperature sensitive element disposed within a first area; a piston coupled to the temperature sensitive element, the piston extending through a wall to a second area, wherein the first area is at a higher temperature than the second area; and a valve arrangement disposed in the second area and actuated by a distal end portion of the piston, the valve arrangement tangentially injecting a supply of cooling air through an angled orifice from the second area into the first area in response an increase in temperature in the first area.

A second aspect of the disclosure provides a passive flow modulation device, including: a temperature sensitive element; a piston coupled to the temperature sensitive element, the piston including a head section, wherein the temperature sensitive element and the piston are disposed in a first area; and an orifice, extending from a second area into the first area, for supplying a flow of cooling air from the second area to the first area, wherein the first area is at a higher temperature than the second area; wherein the temperature sensitive element enlarges or contracts to selectively position the head of the piston over a portion of the aperture to control the flow of cooling air from the second area into the first area.

A third aspect of the disclosure provides a cooling system for a turbine, including: an orifice located between a first area and a second area of the turbine, wherein the first area of the turbine is at a higher temperature than the second area of the turbine; a passive flow modulation device disposed adjacent the orifice for directing a flow of cooling air through the orifice from the second area of the turbine to the first area of the turbine, the passive flow modulation device including: a temperature sensitive element disposed within the first area; a piston coupled to the temperature sensitive element, the piston extending through a wall to the second area; and a valve arrangement disposed in the second area and actuated by a distal end portion of the piston, the valve arrangement selectively directing the flow of cooling air through the orifice from the second area into the first area in response a change in temperature in the first area; or a temperature sensitive element; and a piston coupled to the temperature sensitive element, the piston including a head section, wherein the temperature sensitive element and the piston are disposed in the first area;

wherein the temperature sensitive element enlarges or contracts in response to a change in temperature in the first area to selectively position the head of the piston over a portion of the aperture to control the flow of cooling air from the second area into the first area.

The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawing that depicts various embodiments of the disclosure.

FIG. 1 is a schematic diagram of a gas turbine system according to embodiments.

FIG. 2 is a cross-sectional view of a rotor, stator, and a plurality of passive flow modulation (PFM) devices according to embodiments.

FIG. 3 depicts a PFM device in a closed position according to embodiments.

FIG. 4 depicts the PFM device of FIG. 3 in an open position according to embodiments.

FIG. 5 depicts a graph of the flow modulation provided by the PFM device of FIGS. 3 and 4 according to embodiments.

FIG. 6 depicts a PFM device in a reduced flow position according to embodiments.

FIG. 7 depicts the PFM device of FIG. 6 in a full flow position according to embodiments.

FIG. 8 depicts a graph of the flow modulation provided by the PFM device of FIGS. 6 and 7 according to embodiments.

FIG. 9 depicts a binary PFM device in a non-flow position according to embodiments.

FIG. 10 depicts a binary PFM device in a full-flow position according to embodiments.

FIG. 11 depicts a graph of the flow modulation provided by the binary PFM device of FIGS. 9 and 10 according to embodiments.

It is noted that the drawing of the disclosure is not to scale. The drawing is intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawing, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The disclosure relates generally to turbomachines, and more particularly, to passive flow modulation of cooling flow into a cavity.

In the Figures, for example in FIG. 1, the “A” axis represents an axial orientation. As used herein, the terms “axial” and/or “axially” refer to the relative position/direction of objects along axis A, which is substantially parallel with the axis of rotation of the turbomachine (in particular, the rotor section). As further used herein, the terms “radial” and/or “radially” refer to the relative position/direction of objects along an axis (r), which is substantially perpendicular with axis A and intersects axis A at only one location. Additionally, the terms “circumferential” and/or “circumferentially” refer to the relative position/direction of objects along a circumference (c) which surrounds axis A but does not intersect the axis A at any location.

Referring now to the drawings, in which like numerals refer to like elements throughout the several views, FIG. 1 shows a schematic view of a gas turbine system 2 as may be used herein. The gas turbine system 2 may include a compressor 4. The compressor 4 compresses an incoming flow of air 6. The compressor 4 delivers a flow of compressed air 8 to a combustor 10. The combustor 10 mixes the flow of compressed air 8 with a pressurized flow of fuel 12 and ignites the mixture to create a flow of combustion gases 14. Although only a single combustor 10 is shown, the gas turbine system 2 may include any number of combustors 10. The flow of combustion gases 14 is in turn delivered to a turbine 16. The flow of combustion gases 14 drives the turbine 16 to produce mechanical work. The mechanical work produced in the turbine 16 drives the compressor 4 via a shaft 18, and may be used to drive an external load 20, such as an electrical generator and/or the like.

A cross-sectional view of a turbine rotor 22 rotating within a stator 24 (e.g., along axis A) during operation of a gas turbine system 2 (FIG. 1) is depicted in FIG. 2. A rotating flow of air 28 is produced in a wheelspace cavity 30 within the stator 24 during rotation of the rotor 22. A plurality of orifices 34 are circumferentially positioned about the stator 24. Cooling air 32 is tangentially injected via the plurality of orifices 34 into the wheelspace cavity 30 in a direction of rotation of the rotor 22 from a “cold” area (e.g., outside of the stator 24 in this example) to a “hot” area (e.g., the wheelspace cavity 30). The cooling air 32 may be generated for example by a compressor 4 of a gas turbine system 2 (FIG. 1). The orifices 34 may be used, for example, as pre-swirl orifices and/or flow inducers in manner known in the art. According to embodiments, at least one of the plurality of orifices 34 is provided with a passive flow modulation (PFM) device 36, 38, or 40 for selectively controlling the amount of cooling air 32 that is allowed to pass through the orifice 34 into the wheelspace cavity 30.

According to embodiments, a PFM device 36, 38 may be used in series with an orifice 34 to variably control the flow of cooling air 32 passing through the orifice 34 into the wheelspace 30 (e.g., from a cold area to a hot area). For example, the PFM device 36, 38 may initiate the flow of cooling air through the orifice 34, and then increase and accelerate the flow of cooling air 32 exiting the orifice 34 into the wheelspace cavity 30 to or close to the speed of rotation of the rotor 22. Each orifice 34 includes a defined effective throat area Ae and exit angle a to provide a flow path such that the exit velocity and orientation of the air flow provides optimal heat transfer efficiency in the wheelspace cavity 30. The PFM device 36, 38 provides cooling flow savings across the operating range of the turbine 16 and improves the output and efficiency of the turbine 16.

According to other embodiments, a binary PFM device 40 may be used in series with an orifice 34 to binarily control the flow of cooling air 32 passing through the orifice 34 into the wheelspace cavity 30. In a closed position, cooling air 32 is prevented from flowing through the orifice 34 into the wheelspace cavity 30. In an open position, the binary PFM device 40 delivers a specific flow of cooling air to the wheelspace cavity 30. Turbine performance is improved, since the binary PFM device 40 is closed during most turbine operating modes except when high temperatures are predicted or measured in the wheelspace cavity 30.

One or more of the orifices 34 may provide a continuous (e.g., unmodulated) flow of cooling air 32 into the wheelspace cavity 30. Such an orifice 34 is depicted in the lower section of FIG. 2.

The PFM device 36 according to embodiments is depicted in FIGS. 3 and 4. The PFM device 36 is in a closed position in FIG. 3 and in an open position in FIG. 4. In embodiments, some of the components of the PFM device 36 are located in a cold area (e.g., outside of the stator 24), while other components are disposed within a hot area (e.g., the wheelspace cavity 30).

The PFM device 36 includes a valve system 42 positioned in a cold area 44. The valve system 42 includes at least one gas inlet port 46 (FIG. 4) and a gas outlet port 48. A conduit 50 fluidly couples the gas outlet port 48 of the valve system 42 to the orifice 34. An adapter/connector 52 couples the conduit 50 to the stator 24.

A temperature sensitive element 54 disposed within a hot area (e.g., the wheelspace cavity 30) may be used for actuating the PFM device 36. In embodiments, the temperature sensitive element 54 may include a housing 56 containing a thermally expandable material 58. The thermally expandable material 58 may include, for example, a silicon heat transfer fluid or any other suitable thermally expandable material that is stable at the operating temperatures of the turbine 16 (e.g., up to 1300° F.). In other embodiments, the temperature sensitive element 54 may include, for example, a bimetallic element or other type of arrangement that changes size and/or shape in response to a change in temperature.

The thermally expandable material 58 within the housing 56 engages a head 59 of a piston 60, which extends through the stator 24 to a cold area 44. In embodiments, the valve system 42 includes a valve disc 62 that is attached to a distal end of the piston 60. Opposing outer side surfaces 64 (FIG. 4) of the valve disc 62 are configured to mate with corresponding surfaces of a valve seat 66 of the valve system 42. In further embodiments, other valve mechanisms such as, for example, a spring-loaded pintle, a ball and stopper, a butterfly plate valve, and/or the like may be used.

The PFM device 36 is shown in a closed configuration in FIG. 3. That is, in the closed configuration, at least a portion of the outer side surfaces 64 (FIG. 4) of the valve disc 62 engage the valve seat 66 of the valve system 42. In the closed configuration, cooling air 32 is prevented from flowing from a colder area 44, outside of the stator 24, through the conduit 50 and the orifice 34 into a hotter area (e.g., the wheelspace cavity 30).

Referring now to FIG. 4, an increase in temperature in the wheelspace cavity 30 causes an enlargement of the thermally expandable material 58 within the housing 56. As a result, the thermally expandable material 58 expands and forces the head 59 of the piston 60 downward. The displacement of the piston 60 forces the valve disc 62 attached to the end of the piston 60 away from the valve seat 66 as indicated by arrow 70. When the outer side surfaces 64 of the valve disc 62 no longer contact the valve seat 66, a flow of cooling air 32 begins to flow from the gas inlet port 46 through the gas outlet port 48, conduit 50, and orifice 34, into the wheelspace cavity 30. The flow of cooling air 32 increases as the valve disc 62 moves farther away from the valve seat 66 (as the temperature increases further) as more flow area is provided between the outer side surfaces 64 of the valve disc 62 and the valve seat 66.

A graph of the flow modulation provided by the PFM device 36 is illustrated in FIG. 5. As shown, the ratio of the pressure (P3) in the orifice 34 and the pressure (P2) in the wheelspace cavity 30, as well as the air mass flow (qm) through the orifice 34, increases as the temperature (T1) and turbine load (GT load) increase. Arrow 74 indicates a target pressure ratio (P3/P2) and air mass flow (qm) for optimized cooling efficiency for an illustrative turbine (e.g., turbine 16). As indicated by arrow 76, the PFM device 36 provides a substantial cooling flow savings across much of the operating range of the turbine as compared to a fixed flow, which improves the output and efficiency of the turbine.

The PFM device 38 according to embodiments is depicted in FIGS. 6 and 7. The PFM device 38 is in a reduced flow position in FIG. 6 and in a full flow position in FIG. 6. In embodiments, the PFM device 38 is disposed within the wheelspace cavity 30 (e.g., a hot area).

The PFM device 38 includes a temperature sensitive element 78 disposed within the wheelspace cavity 30. In embodiments, the temperature sensitive element 78 includes a housing 80 partially filled with a thermally expandable material 84. The thermally expandable material 84 may include, for example, a silicon heat transfer fluid or any other suitable thermally expandable material that is stable at the operating temperatures of the turbine 16. In other embodiments, the temperature sensitive element 78 may include, for example, a bimetallic element or other type of arrangement that changes size and/or shape in response to a change in temperature.

A piston 86 is coupled to a movable shelf 88. A head 90 of the piston 86 extends at least partially over an exit 92 of an orifice 34. The distal end surface 94 of the head 90 of the piston 86 may have an angled configuration corresponding to the flow angle a of cooling air 32 through the orifice 34 into the wheelspace cavity 30. The angled configuration of the distal end surface 94 of the head 90 of the piston 86 helps to direct the flow of, and maintain the exit angle of, cooling air 32 into the wheelspace cavity 30. Other configurations of the end surface 94 of the head 90 of the piston 86 (e.g., perpendicular to the displacement direction of the piston 86) may also be used.

A biasing member 96 (e.g., a spring) biases the movable shelf 88 and piston 86 towards the exit 92 of the orifice 34 as indicated by arrow 98. In the configuration depicted in FIG. 6, the head 90 of the piston 86 extends at least partially over the exit 92 of the orifice 34. This reduces the flow of cooling air 32 that can pass through the orifice 34 into the wheelspace cavity 30.

Referring now to FIG. 7, an increase in temperature in the wheelspace cavity 30 causes an expansion of the thermally expandable material 84 within the housing 80 and a corresponding displacement of the piston 86 in direction 100. The force applied by the piston 86 counteracts the biasing force applied by the biasing member 96 and forces the movable shelf 88 and piston 86 in direction 100. As indicated by arrow 102, the expansion of the thermally expandable material 84 displaces the head 90 of the piston 86 away from the exit 92 of the orifice 34. Since the head 90 of the piston 86 is now blocking less of the exit 92 of the orifice 34, a larger flow of cooling air 32 can pass from the cold area outside of the stator 24 through the orifice 34 into the wheelspace cavity 30. The flow of cooling air 32 continues to increase as the temperature within the wheelspace cavity 30 increases, which causes additional displacement of the head 90 of the piston 86 away from the exit 92 of the orifice 34. In FIG. 7, the exit 92 of the orifice 34 is fully open.

A graph of the flow modulation provided by a PFM device 38 is illustrated in FIG. 8. As shown, the effective flow area (Ae) and the air mass flow (qm) of the cooling air 32 through the orifice 34 increase as the temperature (T1) and turbine load (GT load) increase. Arrow 174 indicates a target effective flow area (Ae) and air mass flow (qm) for optimized cooling efficiency for an illustrative turbine (e.g., turbine 16). As indicated by arrow 176, the PFM device 38 provides a substantial cooling flow savings across much of the operating range of the turbine as compared to a fixed flow, which improves the output and efficiency of the turbine.

The binary PFM device 40 according to embodiments is depicted in FIGS. 9 and 10. The PFM device 40 is in non-flow position in FIG. 9 and in a full-flow position in FIG. 10. In embodiments, the PFM device 40 is disposed in a cold area (e.g., outside the stator 24).

As depicted in FIGS. 9 and 10, the binary PFM device 40 includes a temperature sensitive pilot valve 100 and a pressure sensitive main valve 102. The temperature sensitive pilot valve 100 is configured to open at a predetermined temperature, which causes a pressurization of the pressure sensitive main valve 102. The pressurization of the pressure sensitive main valve 102 actuates the pressure sensitive main valve 102 to a full open position. To this extent, the pressure sensitive main valve 102 is either full open or full closed.

The temperature sensitive pilot valve 100 includes at least one gas inlet port 104 and a gas outlet port 106 (FIG. 10). A temperature sensitive element 108 for actuating the temperature sensitive pilot valve 100 is located within a housing 110. In embodiments, the housing 110 is partially filled with a thermally expandable material 114. The thermally expandable material 114 may include, for example, a silicon heat transfer fluid or any other suitable thermally expandable material that is stable at the operating temperatures of the turbine 16). In other embodiments, the temperature sensitive element 114 may include, for example, a bimetallic element or other type of arrangement that changes size and/or shape in response to a change in temperature.

The thermally expandable material 114 engages a head 112 of a piston 116. A valve disc 118 is attached to a distal end of the piston 116. In the non-flow state, opposing outer side surfaces of the valve disc 118 mate with corresponding surfaces of a valve seat 120 (FIG. 10). In further embodiments, other valve mechanisms such as, for example, a spring-loaded pintle, a ball and stopper, a butterfly plate valve, and/or the like may be used.

The pressure sensitive main valve 102 includes at least one gas inlet port 122 and a gas outlet port 124 (FIG. 10). A pressure sensitive element 126 for actuating the pressure sensitive main valve 102 is located within a housing 128. In embodiments, the pressure sensitive element 126 may include a bellows 130 (or other expandable element (e.g., a diaphragm)) that is fluidly coupled to the gas outlet port 106 of the temperature sensitive pilot valve 100.

The bellows 130 is coupled to a piston 132. A valve disc 134 is attached to a distal end of the piston 132. A weep hole 136, which extends through the piston 132 and valve disc 134, fluidly couples the bellows 130 and the gas outlet port 124. The weep hole 136 releases pressure in the bellows 130 when the temperature sensitive pilot valve 100 closes. In the non-flow state, opposing outer side surfaces of the valve disc 134 mate with corresponding surfaces of a valve seat 138, preventing cooling air 32 from flowing from the gas inlet port(s) 122 through the gas outlet port 124 into the orifice 34 and wheelspace cavity 130. In further embodiments, other valve mechanisms such as, for example, a spring-loaded pintle, a ball and stopper, a butterfly plate valve, and/or the like may be used.

Referring now to FIG. 10, an increase in temperature in the cold area surrounding the binary PFM device 40 causes an expansion of the thermally expandable material 114 within the housing 110. The expansion of the thermally expandable material 114 within the housing 110 displaces the valve disc 118 attached to the end of the piston 116 away from the valve seat 120. When the outer side surfaces of the valve disc 118 no longer contact the valve seat 120, ambient air passes through the gas inlet port(s) 104 and the gas outlet port 106 into the bellows 130. This pressurizes the bellows 130.

The pressurization causes the bellows 130 to expand, displacing the attached piston 132 outward toward the gas outlet port 124. In response to the outward displacement of the piston 132, the valve disc 134 is displaced away from the valve seat 138, allowing cooling air 32 to pass from the gas inlet port(s) 122, through the gas outlet port 124 and the orifice 34, into the hot area (e.g., the wheelspace cavity 30).

A graph of the flow modulation provided by the binary PFM device 40 is illustrated in FIG. 11. As shown, the air mass flow (qm) through the orifice 34 at temperatures above the actuation temperature of the temperature sensitive pilot valve 100 is the same as a fixed flow orifice 34. At temperatures under the actuation temperature, as indicated by arrow 150, the binary PFM device 40 provides a substantial cooling flow savings across much of the operating range of the turbine, which improves the output and efficiency of the turbine.

In various embodiments, components described as being “coupled” to one another can be joined along one or more interfaces. In some embodiments, these interfaces can include junctions between distinct components, and in other cases, these interfaces can include a solidly and/or integrally formed interconnection. That is, in some cases, components that are “coupled” to one another can be simultaneously formed to define a single continuous member. However, in other embodiments, these coupled components can be formed as separate members and be subsequently joined through known processes (e.g., fastening, ultrasonic welding, bonding).

When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element, it may be directly on, engaged, connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A passive flow modulation device, comprising: a temperature sensitive element disposed within a first area; a piston coupled to the temperature sensitive element, the piston extending through a wall to a second area, wherein the first area is at a higher temperature than the second area; and a valve arrangement disposed in the second area and actuated by a distal end portion of the piston, the valve arrangement tangentially injecting a supply of cooling air through an angled orifice from the second area into the first area in response an increase in temperature in the first area.
 2. The passive flow modulation device according to claim 1, wherein the first area and the second area are located within a turbine.
 3. The passive flow modulation device according to claim 2, wherein the first area is disposed between a stator and rotor of the turbine.
 4. The passive flow modulation device according to claim 2, wherein the angled orifice further comprises a pre-swirl orifice or a flow inducer.
 5. The passive flow modulation device according to claim 2, wherein the first area comprises a wheelspace cavity of the turbine.
 6. The passive flow modulation device according to claim 1, wherein the first area contains a rotating flow of air, and wherein the supply of cooling air is injected into the first area through the angled orifice in a direction of rotation of the rotating flow of air.
 7. The passive flow modulation device according to claim 1, wherein the supply of cooling air injected into the first area increases in response to a further increase in the temperature in the first area.
 8. The passive flow modulation device according to claim 1, wherein the temperature sensitive element comprises a housing containing a thermally expandable material.
 9. A passive flow modulation device, comprising: a temperature sensitive element; a piston coupled to the temperature sensitive element, the piston including a head section, wherein the temperature sensitive element and the piston are disposed in a first area; and an orifice, extending from a second area into the first area, for supplying a flow of cooling air from the second area to the first area, wherein the first area is at a higher temperature than the second area; wherein the temperature sensitive element enlarges or contracts to selectively position the head of the piston over a portion of the aperture to control the flow of cooling air from the second area into the first area.
 10. The passive flow modulation device according to claim 9, wherein the orifice comprises an angled orifice, and wherein a distal end of the head of the piston includes an angled surface.
 11. The passive flow modulation device according to claim 10, wherein the angled surface of the head of the piston has a shape corresponding to a flow angle of the cooling air through the angled orifice.
 12. The passive flow modulation device according to claim 9, wherein the first area and the second area are located within a turbine.
 13. The passive flow modulation device according to claim 12, wherein the first area comprises a wheelspace cavity of the turbine.
 14. The passive flow modulation device according to claim 9, wherein the orifice comprises a pre-swirl orifice or a flow inducer.
 15. The passive flow modulation device according to claim 9, wherein the first area contains a rotating flow of air, and wherein the flow of cooling air is injected into the first area through the angled orifice in a direction of rotation of the rotating flow of air.
 16. The passive flow modulation device according to claim 9, wherein the temperature sensitive element comprises a housing containing a thermally expandable material.
 17. A cooling system for a turbine, comprising: an orifice located between a first area and a second area of the turbine, wherein the first area of the turbine is at a higher temperature than the second area of the turbine; a passive flow modulation device disposed adjacent the orifice for directing a flow of cooling air through the orifice from the second area of the turbine to the first area of the turbine, the passive flow modulation device including: a temperature sensitive element disposed within the first area; a piston coupled to the temperature sensitive element, the piston extending through a wall to the second area; and a valve arrangement disposed in the second area and actuated by a distal end portion of the piston, the valve arrangement selectively directing the flow of cooling air through the orifice from the second area into the first area in response a change in temperature in the first area; or a temperature sensitive element; and a piston coupled to the temperature sensitive element, the piston including a head section, wherein the temperature sensitive element and the piston are disposed in the first area; wherein the temperature sensitive element enlarges or contracts in response to a change in temperature in the first area to selectively position the head of the piston over a portion of the aperture to control the flow of cooling air from the second area into the first area.
 18. The cooling system according to claim 17, wherein the orifice comprise an angled orifice, and wherein the angled orifice comprises a pre-swirl orifice or a flow inducer.
 19. The cooling system according to claim 17, wherein the first area comprises a wheelspace cavity of the turbine.
 20. The cooling system according to claim 17, wherein the first area contains a rotating flow of air, and wherein the flow of cooling air is directed from the second area into the first area through the orifice in a direction of rotation of the rotating flow of air. 